This invention relates generally to sliding-gate valves and more particularly to improvements therein facilitating use with highly abrasive solids.
This invention was developed in response to a need for a reliable and long-lived block valve for controlling the flow of abrasive solids--e.g., coal ash--through a vertically disposed outlet line connected to a hopper. The design requirements for the desired valve specified that it should operate for long periods without jamming resulting from buildup of particulates and with only minimal abrasion of its sealing surfaces. Conventional valves were found to be deficient with respect to either or both of these requirements.
Conventional sliding-gate valves for use with abrasive solids include the valve described in U.S. Pat. No. 3,918,471, issued to M. P. Bedner on Nov. 11, 1975. That valve includes a slidable gate which is mounted for reciprocation in a leaktight valve body; the body is pressurized with a purge gas. Another sliding-gate valve for use with abrasive solids is disclosed in U.S. Pat. No. 4,174,728 issued to G. B. Usnick et al on Nov. 20, 1979. That valve includes a reciprocatable gate whose sealing surfaces are shielded by the valve seats when the gate is in its fully open and fully closed position. The gate-to-seat clearances are swept by an inflowing purge gas while the gate is in transit.
The known art also includes a metering valve for receiving powder from a hopper and intermittently dispensing a fixed volume of the same. The metering valve includes an upper disc having a marginal portion thereof fitted between the top and center seats. The disc is rotatable between positions where an aperture in its margin is either in register with and out of register with the seats. A similarly rotatable lower disc is fitted between the center and bottom seats. With the lower disc in closed position and the upper disc in open position, powder accumulates in the volume defined by the discs and seats. The upper disc then is rotated closed to isolate the valve from the hopper, following which the lower disc is rotated open to dispense the trapped volume of powder. The discs are at all times in contact with their respective stationary seats.